Abstract

Net photosynthetic oxygen evolution in Amphiroa anceps (Lamarck) Decaisne is inhibited at high oxygen concentrations. Photosynthesis is highest between pH 6.5 and 7.5. At pH 9 to 10 there is still a significant photosynthetic rate, suggesting that this alga can use HCO - 3 as a substrate for photosynthesis. At pH 7.0 to 8.5, the photosynthetic rate saturates at a total inorganic carbon concentration (ΣCi) greater than 3 mM. At pH 8.5 and 8.8, calcification rate continues to increase with increasing concentration of ΣCi. Between pH 7 and 9, the calcification rate in the light in A. foliacea Lamouroux is proportional to the photosynthetic rate, whereas at higher pH where the photosynthetic rate is very low, the calcification rate is stimulated by the higher concentration of CO 2- 3 ion. At all pH values examined, the calcification rate of living plants in the dark and of dead plants is directly proportional to the CO 2- 3 ion concentration, suggesting little metabolic involvement in calcification processes in the dark, whereas calcification in live A. foliacea in the light is influenced both by the photosynthetic rate and the CO 2- 3 ion concentration in the medium.